How to Calculate Valency with Examples and Chart
Valency is essential in chemistry and helps students understand various practical and theoretical applications related to this topic.
What is Valency in Chemistry?
Valency in chemistry refers to the ability of an atom to combine with other atoms based on the number of electrons it can lose, gain, or share. The concept of valency helps us predict the number of bonds an element can form, making it important for studying chemical reactions, chemical bonding, and formation of compounds. Valency plays a key role in chapters related to atomic structure, periodic trends, and chemical formulas.
Molecular Formula and Composition
The term “valency” does not have a specific molecular formula. Instead, it is a property or number associated with each element showing how many chemical bonds its atoms can form. For example, the valency of hydrogen is 1, oxygen is 2, and carbon is 4. This concept falls under the topic of atomic properties and is useful while writing molecular formulas like H2O and CO2.
Preparation and Synthesis Methods
Valency is not something you prepare or synthesize, but rather a number that depends on the arrangement of electrons in an atom's outermost shell. You can determine valency using the periodic table or electron configuration rules. Vedantu often provides easy tricks and charts to help students find valency quickly in live classes and notes.
Frequent Related Errors
- Confusing valency with the number of valence electrons (they are not always equal).
- Mixing up valency with oxidation number or state.
- Forgetting that some elements have variable valency (such as iron: 2 or 3).
Valency Chart/Table
| Element | Symbol | Valency |
|---|---|---|
| Hydrogen | H | 1 |
| Helium | He | 0 |
| Lithium | Li | 1 |
| Beryllium | Be | 2 |
| Boron | B | 3 |
| Carbon | C | 4 |
| Nitrogen | N | 3 |
| Oxygen | O | 2 |
| Fluorine | F | 1 |
| Neon | Ne | 0 |
| Sodium | Na | 1 |
| Magnesium | Mg | 2 |
| Aluminium | Al | 3 |
| Silicon | Si | 4 |
| Phosphorus | P | 3 |
| Sulfur | S | 2 |
| Chlorine | Cl | 1 |
| Argon | Ar | 0 |
| Potassium | K | 1 |
| Calcium | Ca | 2 |
How to Calculate Valency
Valency is mostly determined by the number of electrons in the outermost shell of an atom. If the outer shell has less than or equal to 4 electrons, valency equals the number of these electrons. If it has more than 4, valency equals 8 minus the number of outer electrons.
Steps to calculate valency:
1. Find the element's group number (main group elements) or note the electron configuration.2. Count the electrons in the outermost shell.
3. If that number is ≤ 4, valency = (number of outer electrons).
4. If it's > 4, valency = 8 minus (number of outer electrons).
Examples:
1. For Oxygen (atomic number 8): Outer shell has 6 electrons. Valency = 8 – 6 = 2.2. For Nitrogen (atomic number 7): Outer shell has 5 electrons. Valency = 8 – 5 = 3.
3. For Sodium (atomic number 11): Outer shell has 1 electron. Valency = 1.
Transition elements and some main-group elements may have variable valency.
Valency Examples (Application)
- Water (H2O): Hydrogen valency 1, Oxygen valency 2 — two hydrogens combine with one oxygen.
- Carbon Dioxide (CO2): Carbon valency 4, Oxygen valency 2 — one carbon combines with two oxygens.
- Ammonia (NH3): Nitrogen valency 3, Hydrogen valency 1 — one nitrogen with three hydrogens.
Uses of Valency in Real Life
Valency is widely used in writing chemical formulas, predicting reactions, designing compounds in medicines, fertilizers, and materials. It helps scientists and students understand how atoms join to form molecules in everyday objects.
Relation with Other Chemistry Concepts
Valency is closely related to atomic structure and oxidation number. It works with the octet rule and helps you understand chemical bonding and types of chemical reactions. Knowing valency makes it easy to predict the formulae and properties of new compounds.
Step-by-Step Reaction Example
1. Take the elements carbon and oxygen.2. Carbon's valency is 4, and oxygen's is 2.
3. To saturate all bonds, two oxygens are required for one carbon (CO2).
4. The chemical equation is: C + O2 → CO2
5. Both carbon and oxygen use their valency to form stable bonds in this molecule.
Lab or Experimental Tips
Remember valency by the rule of “eight” (octet rule) — atoms want to complete their shell with 8 electrons (or 2 for hydrogen and helium). Vedantu educators use tricks like periodic table group numbers to find valency at a glance.
Try This Yourself
- Write the formula for a compound formed by magnesium (Mg) and chlorine (Cl).
- Determine the valency of phosphorus from its electron configuration.
- Give two daily examples where understanding valency is useful.
Final Wrap-Up
We explored valency—its definition, calculation, examples, and connections to other chemistry ideas. Understanding valency helps you write correct formulas, explain reactions, and score higher in chemistry. Keep practicing with Vedantu resources for clarity and mastery of chemistry basics.
FAQs on What is Valency in Chemistry?
1. What does valency mean in simple terms?
In chemistry, valency is the combining power of an element. It tells you how many chemical bonds an atom of that element can form with other atoms. This ability depends on the number of electrons it needs to gain, lose, or share to achieve a stable state, like that of a noble gas.
2. How can you find the valency of an element?
You can determine valency from the number of valence electrons (electrons in the outermost shell):
If an atom has 1, 2, 3, or 4 valence electrons, its valency is equal to that number.
If an atom has 5, 6, or 7 valence electrons, its valency is calculated as 8 minus the number of valence electrons.
Noble gases have a full outer shell (8 valence electrons), so their valency is typically zero.
3. What is the valency of common elements like carbon, oxygen, and sodium?
The valency of these common elements is:
Carbon (C): Valency is 4, as it has 4 valence electrons and usually shares them to form four bonds.
Oxygen (O): Valency is 2, as it has 6 valence electrons and needs to gain 2 more (8 - 6 = 2).
Sodium (Na): Valency is 1, as it has 1 valence electron and easily loses it.
4. What is the difference between valency and valence electrons?
While related, they are not the same. Valence electrons are the actual electrons present in an atom's outermost shell. Valency is the number of bonds an atom will form, which is a property derived from its need to lose, gain, or share those valence electrons.
5. How does valency help in writing the chemical formula for a compound?
Valency is crucial for predicting chemical formulas. By knowing the valencies of two elements, you can determine the ratio in which they combine. For example, magnesium (valency 2) and chlorine (valency 1) combine in a 1:2 ratio to form MgCl₂, balancing out their combining capacities.
6. Can an element have more than one valency?
Yes, some elements, especially transition metals, can show variable valency. This means they can form different numbers of bonds depending on the chemical environment. For example, iron (Fe) can have a valency of 2 in some compounds (like FeCl₂) and 3 in others (like FeCl₃).
7. How is valency different from oxidation state?
Valency is a number that simply indicates how many bonds an atom can form, and it does not have a positive or negative sign. The oxidation state, however, represents the hypothetical charge an atom would have if all its bonds were completely ionic. It can be positive, negative, or zero.
8. Why is understanding valency important in chemistry?
Understanding valency is fundamental because it helps you:
Predict how different elements will combine.
Write correct chemical formulas for compounds.
Grasp the basic principles of chemical bonding and reactions.
9. How does an element's position in the periodic table relate to its valency?
An element's position, specifically its group number, gives a strong clue about its valency. For main group elements, the valency is often related to the group number. For instance, elements in Group 1 have a valency of 1, and elements in Group 17 (halogens) also have a valency of 1 (8 - 7 = 1).
